What’s humidity got to do with my piano?

When we are talking to our prospective customers, not only do we help our customers choose between different brands and models of piano, but we offer advice on the proper care and maintenance of these beautiful instruments. Quite often customers are unaware of the negative impact that adverse humidity conditions can have on an acoustic piano so we look to help them avoid the potential pitfalls at the point of purchase.

Pianos are ‘happiest’ in atmospheric conditions in which people feel comfortable i.e. not too high or low relative humidity or extreme temperatures. If you consider that the primary material used in a piano is wood, then it is not surprising that humidity plays such a huge part in the proper care and maintenance of your instrument! 

Felt, cloth and the precision wood parts used in critical parts of the piano, such as the action, are extremely sensitive to the levels of and variations in temperature and relative humidity. Too high humidity can result in the slight swelling of parts causing a sluggish hammer action, sticking keys, unclear tones, as well as rusting of internal parts. Too little humidity leads to the wooden and felt components slightly shrinking causing stress in the structure and the regulation of the action to change. 

In the same way that a brand new car requires time to run in, your new piano will take some time to settle in and reach its optimum performance. The piano will take some time to acclimatise to the atmospheric conditions of your house, as well as for the many mechanical parts of the action to ‘bed in’. This may result in you experiencing some minor teething issues with your instrument. This may include inconsistencies in the tonal quality and tuning, and the sensation that some notes occasionally play less reliably or feel strange. This is perfectly normal and should start to settle down over the first few weeks of the piano’s life, but the process may take longer at times of the year where the weather is changeable. It is worth keeping a note of any issues that persist so that you can inform our Tuning and Repairs department (or your own piano tuner) before the piano’s first tuning. 

What is relative humidity?

Relative humidity is the ratio of how much moisture is in the air compared to the maximum amount of moisture the air can hold. The absolute amount of water that the air can hold varies depending on its temperature - the warmer the air, the more moisture it can hold. This means that in good weather, the sun is blasting down and heating up the air enabling it to hold more moisture than before. This change actively decreases the ratio of how much water is currently in the air to what it can actually hold, therefore creating a much drier environment for your piano.

On the other hand, cooler air can hold less moisture. This means that if warmer air cools by only a couple of degrees the relative humidity can rise significantly.

When the air has lower relative humidity, this in effect draws moisture out of the wood in your piano causing it to shrink/contract. When the humidity increases again, this allows the wood to absorb moisture causing the wood to expand. It is this constant change in relative humidity that affects the tuning of the piano as well as the regulation of the action. When the humidity is extreme - too high or too low for extended periods or wildly oscillating it can cause irreversible structural damage to your piano. This can cause the wood to crack, split and even warp, regardless of whether the piano is a budget piano or a handmade concert grand piano made in Austria!

What should the relative humidity be?

Most piano manufacturers recommend keeping pianos between 40-60% relative humidity, although extreme change and sudden variation even, within this range, should be avoided. 

This consideration is particularly important during winter and extended cold weather episodes when heated rooms can become extremely dry. Rooms that have underfloor or forced air heating,  can also result in lower relative humidity. 

Whilst a Piano Carpet will help protect the piano from direct radiation from underfloor heating, the overall relative humidity of the air should be monitored and a humidifier and/or a Dampp Chaser system used to ameliorate the excessively dry conditions.

Some areas are prone to higher humidity such as along the coast, in high rainfall areas, in a valley or close to hills, or areas with poor drainage. You should also take care in an area where air exhausts are directed into a room, or in sub-ground level rooms such as basements where there is typically poor air circulation. Rooms that include a kitchen area can also be problematic due to periods of high humidity and higher temperature whilst cooking. Conservatories should be avoided as the large fluctuations in temperature and humidity due to the lack of insulation and direct solar radiation will likely cause extreme conditions and therefore irreversible damage to the piano.

What damage can be caused by extremes of humidity and why is it so bad for my piano?

Below is a birds-eye image of a Schimmel C189T grand piano with the top lid off. We have labelled three major parts that are particularly affected by humidity; the soundboard, bridges and wrest plank which all form critical parts of the acoustic assembly. 

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Damage to the Soundboard

The soundboard is the “speaker” system of an acoustic piano. It is what converts the vibrations from the strings into the beautiful sound that you can hear when you play a key. It needs to be extremely stable and intact to easily allow all of the frequencies to flow through and to become amplified. If there are any cracks, splits or if it becomes warped in any way, this will prevent the frequencies from transmitting through effectively and can cause the sound to be muffled, dull sounding and short in tone as the sound energy is stopped and dissipated.

Damage to the Bridges

Likewise, the bridge also plays a big part in the sound propagation of a piano in the sense that it is the “bridge” that allows the vibrations of the strings to flow through and be transmitted to the soundboard. Bridges play a very important role in keeping the strings in place by using bridge pins, as pictured below. Over time, these bridge pins, which are under extreme lateral pressure from the strings, can start to become unstable as splits open - particularly where the piano has been subject to dry conditions. This can sometimes cause unwanted metallic sounds, a very noticeable change in tone to adjacent notes and poor tuning stability. These symptoms are near to impossible to get rid of without replacing the bridge itself.  Another common problem that can be caused by low humidity is the whole bridge becoming detached from the soundboard. This obviously means there is a gap in the conduit to the soundboard which will cause the piano to have a much weaker sound, poor dynamic range and terrible tuning stability! We have seen this happen in relatively young modern uprights (e.g. 25-year-old Kembles and Yamahas) as well as much older instruments.

Damage to the Wrest plank (pin block)

The wrest plank is possibly the most important component of your piano when it comes to tuning stability. The wrest plank is a thick piece of wood (in more modern pianos this is usually laminated) which the tuning/wrest pins are screwed into. When a tuner comes to tune the piano, they effectively turn these pins which grip onto the wood to keep the strings nice and tight at the appropriate tension. If this plank becomes compromised in any way, then the pins will no longer be able to hold their grip and in turn to hold the tuning of the strings. 

Damage to the casework parts

Extremes of relative humidity can also cause structural problems with a piano’s casework. In the same way that the acoustic body elements of the piano will swell and contract with the changes in humidity, the wooden case parts will also change. Even pianos which are finished in modern high gloss polyester can be damaged with the woodwork swelling causing the polyester to crack and come away from the surface.

Damage to action parts

There are over 10,000 tiny parts in a piano action predominantly made from wood, felt, leather and steel. One of the biggest issues we find with pianos exposed to prolonged periods of high humidity is the action becomes sluggish and heavy. 

In the action, there are points at which parts hinge to ensure that the hammer moves smoothly to hit the strings and so that it returns back fully so the player is able to repeat the note. This “hinge” is known as a centre, which is basically a tiny pin, hinging together the mechanism of the hammer, with a tiny layer of felt surrounding the pin to allow it move smoothly and to reduce any unwanted noise in the action. If this felt absorbs moisture, it will tighten the centre and cause it to be sluggish and stiff. You can see the effects of this in the video taken in a customers home below. 

The hammer should freely swing from side to side ideally three full swings or five to six half swings. This really shows the extent of the exposure to high relative humidity as the hammer in this video doesn't even make it through one swing!

If you take into consideration there are three centres in a piano action, it’s no surprise that it takes a couple of days to fully re-centre a piano action!

Alternatively, prolonged exposure in a dryer environment can cause the action to feel much looser and in worse cases causing the centres to warp and split.

Assessing a piano for part-exchange or buy in - looking for the effects of detrimental humidity 

We are often approached by customers looking to either upgrade from their existing pianos and part exchanging or simply wanting to sell them. Before we fully commit to buying or part-exchanging any piano we have to determine what the likely condition of the instrument is. We can get some ‘clues’ by finding out how old the instrument is, where it has been kept and in what type of conditions throughout its life. It is also useful to know if the vendor is aware of any structural problems with the piano. If their tuner has already told them the piano can no longer be tuned, sadly the likelihood the piano has little or no value. 

Often photos can speak a thousand words and we can get a general feel for its likely condition. On this basis, we can usually give the vendor a guide on what we might be able to offer, however, ultimately we can only really determine the overall condition of an instrument and therefore it’s value if we send a piano technician to inspect the instrument. The technician would normally check the tuning stability first. This is the main ‘Achilles heel’ of a piano - if it can no longer hold a tuning at concert pitch whether it is a Steinway grand piano or relatively new Yamaha upright - it has virtually no value. This is because to replace the wrest plank is major ‘open-heart surgery’ and for most instruments is not economically viable.  The technician would also check the soundboard for any cracks or swelling, the bridges for any fractures or looseness and the iron frame to ensure there are no cracks to be found. They also check for any sign of damp inside the instrument and for any unwanted beasties, such as moths. You can read more on this in another blog soon to be uploaded.


Below is a photograph taken by one of our technicians in a prospective customer's home of a very young (3-year-old), Chinese made, Broadwood self-playing grand piano. You can clearly see that there is a very long crack running along the grain of the soundboard. 

And again here, you can clearly see in this picture taken looking above the piano, that you can actually see light coming through the soundboard. This really is a worst-case scenario and due to the structural damage means the piano is a virtual write off as it is not easily repaired and it would not be economically viable to do so.

The customer, who owned this instrument, purchased this from another piano shop local to them. Unfortunately, they weren't aware of the impact that underfloor heating can have on a piano. Thinking of a hot air balloon, we all know that hot air rises. Placing a grand piano over underfloor heating allows the warm, dry air to rise and effectively pool underneath the soundboard causing it to dry and inevitably split. As mentioned above, you can combat this by using a Piano Carpet *insert link* to help stop the rising heat/dry air from destroying your pride and joy. 

So, how do you measure the relative humidity?

Signs of excess humidity can include sticking keys, a sluggish action, the pitch going sharp - particularly in the middle of the keyboard, corrosion on the strings and you may even smell damp in the air. After prolonged periods in excess humidity, it is also something that you can often see on the inside of your piano with a light dusting of mould and sometimes water stains. 

Looking at the two pictures below, you can quite clearly see signs of mould that have marked the wood on the hammers and at the very back of the keys. 

Signs of low humidity are a lot less obvious to spot, so it is really important to keep an eye on this. You can quite easily check the room relative humidity by using a hygrometer, such as this picture below. These digital hygrometers, which record the maximum and minimum temperatures and relative humidity, are much more accurate and will give you a better understanding of how the conditions change over time with the max and min settings, rather than one-off readings.

These Digital Hygrometers are available for purchase on our website and we have plenty of these in stock available for posting out. We can also give you guidance on the frequency of readings and provide you with some helpful charts to help keep a log.

I have my readings now, so how can I combat the negative effects of excess/low relative humidity? 

It is good practice to treat the room as a whole when you are experiencing problems with extremes or fluctuations in humidity. As the majority of furniture in our homes is also made of wood, they will certainly thank you for it! Us humans also benefit from a ‘healthy’ humidity - very dry air can cause dry itchy skin and the opposite extreme can exacerbate respiratory problems.

The key is to identify how the conditions vary over time and at different times of the year and adjust the environment accordingly.

It seems a lot of piano tuners' advice to their customers is to put a tub of water in the bottom of their piano regardless of knowing what the environmental conditions are. The problem is, many tuners don’t check the humidity by taking any readings and therefore this advice is often misleading and can be incorrect as well as not being the most effective way of adding humidity to the environment if it is relatively dry. We often plead with our customers not to take this advice as gospel and properly diagnose what the conditions are before taking any action! Please check first!

Below is a picture of a lovely customer's piano a few years ago. She had a Yamaha U1X that her piano tuner had advised her to put two 5 litre tubs of water inside the bottom right-hand corner. Whilst the environment may have been relatively dry, his advice on how to ameliorate it was actually incredibly harmful to the piano.  Having such a direct and constant source of very high humidity next to the soundboard caused the wood to expand and because the tubs were then left to dry out, the two extremes caused the wood to contract and split. 

If you know you suffer from low humidity then a concentrated point source of water is best avoided if possible as it can cause differential movement in the wood and damage the piano - as shown above. You will be pleased to hear there are, however, much more effective ways to look after your instrument, which are discussed below. 

Tackling excessively low humidity 

One of the main weapons of choice to combat an excessively dry environment is by using a humidifier which introduces moisture back into the air.

The humidity in our showroom is on the low side, most of the time, so to combat this we have some industrial humidifiers, which would be overkill in your own home. We also have some smaller models which we picked up from Maplins, before they shut down. A customer of ours recently contacted us about what we would recommend. We sent him the specifications of Maplin’s own humidifiers, which he used to source his own. He wrote back to us to say "I have ordered the 'PureMate PM-906 Digital Ultrasonic Cool & Warm Mist Humidifier with Ioniser'.  The company Pure Mate has been very helpful. When it arrives, I will let you know what I think of it. It costs £79.99, with free delivery (a bit extra for delivery to Ulster, Northern Ireland)" We will report back ourselves when we hear from him!

As mentioned earlier, depending on the source of the dry air there are various ways to ameliorate the effects. For direct radiation from underfloor heating, there are different sizes of piano carpets available to suit your pianos needs. The carpet needs to cover the entirety of the “footprint” of the piano to ensure maximum protection, which includes the key bed sticking out of the front of the piano. If you have a smaller upright piano with the “modern” cabinet design, such as the one pictured below, there are smaller mats available for order at £175. 

Likewise, there is also a slightly bigger upright piano carpet for those whose key beds stick out more with the traditional legs and toes, such as in the picture below. These are priced at £200 and also available for order. Click the images to take you to the product on our website. 

For a grand piano, these mats are custom made to order, again to fit the footprint of the instrument, as seen in the image below. It is imperative that the carpet covers the entirety of the soundboard and keybed to prevent any structural damage.  

A common concern from our customers with underfloor heating and these carpets is that they are not particularly glamorous.! There is no denying this! They are, however, thin enough to place a more aesthetically pleasing rug over the top. We know this may not be what you had in mind when you pictured the piano in your underfloor heated home, however, if you are spending a rather large amount of money on a piano, this item is a necessity! 

If you know you suffer from low-humidity, you can purchase a piano humidifier tube. As it explains on our website, the piano humidifier tube is a simple but effective way of adding humidity to the environment within a piano. In many homes with central heating, the relative humidity can drop to levels that can cause structural problems with pianos (i.e. below 40%RH). By using this tube, which is manually soaked in water then placed in the piano, you can effectively create a microclimate in an upright piano. This device looks after the whole of the soundboard unlike the tub of water which will be mainly concentrated in one spot on the bottom right-hand side of the piano. These tubes are priced at £46 and can very easily be fitted inside the bottom of your upright piano. 

You can pick one on our website here

Combating excessively high humidity

At the opposite end of the spectrum, a dehumidifier can be used to reduce the excess humidity in the air of the room as a whole. For upright pianos there are also very low energy heaters that can effectively create a microclimate inside the piano - raising the temperature slightly and therefore driving down the relative humidity of the air inside - more on this below.

There are plenty of dehumidifiers available on the market. Some of the top-end models have built-in humidistats that will automatically control the environment, while the others are much more basic. These devices are generally used to treat the room as a whole, which is definitely advisable for grand pianos and has the added benefit of helping other wooden items in the room like furniture! As we don't sell them at Forsyth, we unfortunately do not have recommendations on particular models, however, there are plenty of reviews out there and devices to suit your budget.

Another way in which to improve your piano's environment is to use a piano specific system such as a Dampp Chaser, low energy heater bar. These are most effective in upright pianos but can be used on grands too.  *insert links*

Like the humidifier bar, the enclosed nature of an upright piano helps to create a microclimate that will protect all the internal guts of the instrument. In their simplest form, the heater bars can be plugged in and you have to decide when to turn it on and off. These are easy to self install and are £52. Alternatively, there is a ‘humidistat’ controlled system which does this for you for £156. You can buy either of these from Forsyths - please give us a ring for further advice, or pick them up on our website here. 

Tackling an environment that suffers from both extremes

In our ‘interesting’ changeable British climate we have the challenge of trying to adjust the environment in response to the variable conditions. In many homes it will tend to be a particular season where you have to work at rectifying the conditions, however, for others you need different tactics for different times of the year. You may, therefore, need more than one weapon of choice!

Alternatively, Dampp Chaser offers a piano specific ‘complete’ climate control system for both grand and upright pianos. Whilst we would always recommend trying to treat the room as a whole with a humidifier/dehumidifier as appropriate, these Dampp Chaser systems help to ameliorate the worst of the conditions. These systems are less effective for grand pianos as you can’t create the same microclimate effect that you can in an upright piano. 

These climate control systems try to protect the piano from the worst extremes of environments that are constantly changing. When the humidity reads above 45% the low emission heater bars will kick in to raise the temperature slightly and therefore reduce the relative humidity. If the relative humidity reads below 45% this will turn on the humidifier system which introduces moisture into the air to protect the piano. The humidity is provided from manually filled water reservoir tanks that are installed in/under the piano. These are available for both upright and grand pianos, starting at £388 for an upright and £422 for grand pianos up to 5ft and £494 for grand up to 6ft. For larger grands, you may need an additional heater bar at the back of the piano. Again these are provided with instructions for self-installation, however, we are able to come and fit these if required at an extra cost and depending on location. You can see these on our website here. 

Need some more advice or help?

Hopefully we’ve not bamboozled you with too much information but hope this document gives you a good understanding of all the things that need to be considered and the best tactics to look after your piano.   We employ a team of piano tuners and piano technicians who can help you maintain your piano and put right many of the effects of challenging environmental conditions. If you do have any further questions, worries, would like to book a visit from a technician or would like to order any of the products above, please email [email protected] or call on 0161 834 3281 extension 5 for more details.